As is well known in the gas turbine engine technology it is desirable to operate the combustor at optimum efficiency while achieving good lean blowout, altitude relight, void of smoke and pollutants while being able to increase the temperature of the hot gases while maintaining the integrity of the combustor liner as well as being cost effective. Scientists and engineers have been experimenting with the designs of the fuel nozzles for many years in attempts to maximize the efficacy of the combustor. This invention constitutes an improvement over the fuel nozzle described in U.S. Pat. No. 5,603,211 granted to Charles B. Graves, the inventor of this patent application, on Feb. 18, 1997 entitled "Outer Shear Layer Swirl Mixer For A Combustor" which is commonly assigned to United Technology Corporation. As disclosed in the U.S. Pat. No. 5,603,211, supra, the fuel nozzle includes a swirler design that includes three air swirling passages, namely, a center duct and two annular ducts located radially outward from the fuel injector. These passages include vanes for swirling the incoming air and are tailored to have significantly different swirl angles to yield low smoke production and high relight stability in high temperature rise combustors. In the construction of the fuel nozzle in the U.S. Pat. No. 5,603,211, supra, the high swirl passage was confined to the vicinity of the fuel injector and a counter-rotating annular passage surround it which provided both the features of a high swirl and low swirl device.
While this structure in the U.S. Pat. No. 5,603,211, supra, produced high swirl angles along the centerline and low swirl angles along the injector prefilmer, in evaluating this device certain disadvantages were noted. Namely, the mixing shear layer between the two counter-rotating passages appeared to impede the transport of the spray to the prefilmer, and in general, the less the amount of flow in the counter rotating passage the better the injector performed. It was also noted that the mixing of the passages produced a pressure loss which dictated that the vane areas needed to be increased to levels larger than what would normally be required in a standard high shear design.
In addition to the above-referred to patent there are a plethora of fuel nozzles that are disclosed in the prior art that include swirlers and injectors for combustors of gas turbine engines and all of which provide recirculation zones for stabilizing combustion. Examples of prior art fuel nozzles are disclosed in U.S. Pat. Nos. Re. 30,160 reissued in Nov. 27, 1979 and granted to Emory, Jr. et al entitled Smoke Reduction Combustion Chamber, U.S. Pat. No. 3,570,242 granted to Leonardi on Mar. 16, 1971, entitled Fuel Premixing For Smokeless Jet Engine Main Burner, U.S. Pat. No. 4,991,398 granted to Clark et al on Feb. 12, 1991 entitled Combustor Fuel Nozzle Arrangement all of which are commonly assigned to United Technologies Corporation, the assignee of this patent application. Additional patents of interests are U.S. Pat. No. 3,853,273 granted to Bahr et al on Dec. 10, 1974 entitled Axial Swirler Central Injection Carburator, U.S. Pat. No. 3,901,446 granted to Petreikis, Jr. on Aug. 26, 1975 entitled Induced Vortex Swirler, U.S. Pat. No. 4,194,358 granted to Stenger on Mar. 25, 1980 entitled Double Annular Combustor Configuration and U.S. Pat. No. 4,842,197 granted to Simon et al on Jun. 27, 1989 entitled Fuel Injection Apparatus And Associated Method.
I have found that I can provide a fuel nozzle having a fuel injector at the center, an inner swirl passage adjacent to the fuel injector and coaxial therewith and an annular swirl passage concentrically mounted relative to the inner passage and having the vanes in the inner swirl passage contoured with a discretely shaped twist which will not only duplicate the advantages of the structure disclosed in the U.S. Pat. No. 5,603,211, supra but will obviate the disadvantages thereof. Obviously, the elimination of the third passage will not only lessen the complexity of the design but also will reduce costs.